The present invention relates to a propellant charge igniter for tank ammunition. More particularly, the present invention relates to a propellant charge igniter for tank ammunition with a combustible metallic igniter tube and a flexible coupling between ignition elements
Conventional high-pressure igniter tubes for tank cannon ammunition are typically made from steel. They are used to contain combustible materials such as benite, which is a mixture of black powder and nitrocellulose. The igniter tube itself is provided with vent holes along its length, and is usually threaded into a primer head assembly which is capable of transmitting energy (i.e. pressure and/or temperature) into the combustible mixture of materials contained within the igniter tube. When the energy induced is sufficient to cause combustion of these materials, an intense flame is produced which issues from the vent holes and into the main propellant charge. The intensity of the flame produced is critical to a rapid ignition of the main propellant charge, and is related to the ability of the igniter tube to contain the combustible material and products of combustion at high pressures (approximately 25-35 MPa).
A rapid and uniform ignition of the main propellant charge is important since it minimizes the time delay between target acquisition and actual launching of a projectile. If the time delay is excessive, the muzzle aim point may no longer coincide with the position of a moving target. Thus, an igniter casing capable of withstanding the high gas pressure of a benite-like material will help improve the performance of the tank gun. Steel igniter tubes are currently used for this reason.
Nevertheless, combustible, low-pressure, cardboard-like igniter tubes containing black powder have been used. These tubes split as the internal pressure rises, and burn along with their combustible contents. Somewhat after these events, the main propellant charge is ignited. As a result, this ignition sequence is several times slower, and less desirable, than the high-pressure benite system previously described
Some high-pressure propellant charge igniters with steel igniter tubes are deployed in combustible external shell casings, which are less rigid than their non-combustible counterparts. As a result, mishandling of such a round can result in stress cracks near the base of the igniter tube, where it joins the primer head assembly. In a high pressure ignition system it is likely that the main charge will then be ignited at the site of the igniter tube fracture, near the base of the round. This in turn can lead to an ignition process whereby the propellant bed is pushed forward, creating a stress wave that is strong enough to break the propellant grains (or sticks) into small pieces (e.g. when the propellant is cold).
A pulverized propellant bed has more surface area for burning, and will therefore yield a shorter duration but higher maximum pressure than if the propellant was unfractured. A sharp pressure rise such as this can crack the barrel or even "blow" the breech. In fact, this was suspected to be the cause of at least one accident several years ago. Attempts have been made to solve this problem by reinforcing the joint between the primer head assembly and the igniter tube.
There are, however, other problems associated with conventional high-pressure ignition systems. These include the hazards and space requirements associated with storing spent casings. The hazards arise out of the steel igniter tubes which protrude from spent casings ejected from the gun. These steel igniter tubes are largely intact and extremely hot. In the confines of a tank, spent casings must be stored in close proximity to the crew, increasing the likelihood that a crew member will come into contact with a hot steel tube. In addition, because of their size, only a small number of casings can be stored before firing must be stopped and the cabin cleared.